1. Field of the Invention
This invention relates to catheter assemblies, and more particularly, to self-inflating or autoinflating balloon catheters within the catheter and balloon assembly, including means for automatically regulating the fluid pressure inside the autoinflating balloon.
2. Description of the Related Art
Catheters have long been used in a wide variety of medical procedures in which the catheter is received in a bodily orifice to conduct fluid by way of the orifice. An example of one such procedure is known as retrograde cardioplegia solution perfusion. The catheter employed is provided with a selectively inflatable cuff or balloon adjacent the distal tip of the catheter. The distal tip is formed with one or more fluid outlets for the discharge of fluid from the catheter assembly. When the distal tip and the balloon are inserted in the coronary sinus and are properly situated, the balloon is inflated to occlude the sinus and to retain the catheter therein. Typically, the catheter and balloon are introduced into the coronary sinus as blood is naturally flowing through it in the opposite direction. Once the balloon has been inflated to occlude the coronary sinus, cardioplegia solution is forced through the catheter to exit through the outlet at the distal tip and perfuse the heart by way of the cardiac veins.
Many different balloon catheter assemblies have been developed for this procedure, but they can be divided between those having manually inflated balloons and those provided with “self-inflating” or “autoinflating” balloons. Manual inflation is accommodated by manufacturing the catheter assembly with a secondary lumen in communication with the interior of the balloon. Autoinflating balloons are automatically inflated by means of a fluid interconnection between the catheter lumen and the interior of the balloon. Most autoinflating balloons are preformed so that the body portion of the balloon extends radially outwardly from the catheter body even in the relaxed condition. However, most manual inflation balloons are formed of an elastomeric material such as silicone so that substantially the entire balloon is tightly received around the body of the catheter in the relaxed position and must be inflated or expanded radially in order to occlude the coronary sinus.
Examples of such catheters are disclosed in U.S. Pat. No. 5,385,548, issued Jan. 31, 1995 to C. R. Williams et al., U.S. Pat. No. 5,197,952, issued Mar. 30, 1993 to S. J. Marcadis et al., and U.S. Pat. No. 4,917,667, issued Apr. 17, 1990 to J. Jackson.
Prior balloon designs may present, one or more of several problems. For example, preformed balloons are typically larger in the relaxed state than the opening of the coronary sinus. Therefore, the balloon is difficult to insert into the coronary sinus and may cause trauma to the tissue as it is inserted. Eliminating the preformed balloon may reduce the trauma the tissue endures during insertion of the balloon. In a catheter having a manually inflated balloon, the balloon may be made of a tightly fitting elastomeric material. Heretofore, however, tightly fitting elastomeric balloons have not been employed in autoinflating catheter balloon assemblies because no effective means were known for controlling the inflation rate of the elastomeric balloon.